Fusor Forums

Hi
I got my self a new toy ,LUDLUM 48-1614 MODEL 15 NEUTRON COUNTER DOSE SURVEY METER 44-7 GM DETECTOR 42-14
Still testing it ,any one have any more information about it, or any one used it before
Thanks in advance

The meter part of your setup is much like the rest of the Ludlum lineup. Calibration is best achieved with a pulser. That lines out the counting. The rest of the setup is done with the tube. He3 tubes have a very low output compared to others. Normally they are set to 2 mV to read the pulse. There is an entire procedure on the site here on how to get the meter settings right with an He3 or BF3 tube. You essentially put the tube in a high gamma field and raise the mV up until you get gamma spikes. Then drop the mV until the gamma is just gone. This should give the settings for neutrons. Of course you need to run the voltage up to the correct range for this to work. The higher the voltage the better the gain. Too high and then cascade breakdown and that is not good.

Thanks Frank
The devices was calibrated by ludlum, but the issue is that ludlum calibrated all items separately!!!
The ludlum attached the calibration certificates (attached)
But when i powered it on the the gama bets worked but it didn't count any neutrons when i switched to n counter.
So i attached the 42-14h neutron detector to my ludlum 2200 adjust the voltage to 1273 volts and input sensitivity to 30 mv
It worked perfectly . And I tested on AmBe source ( tested first with Am241 no counts) ( on gama nearly no counts)
Back ground 5-8 cpm. On AmBe 100 cpm
My issue is how to measure the input sensitivity for this device, i know there is DIS under the calibration cover.
Thanks

They are two separate independent units so as such they will not be calibrated together. The meter is stupid. It does nothing more that count pulses above a threshold voltage. The calibration for the meter then is just to put in a standard number of pulsed above that threshhold and be sure that is the count that the meter is displaying. It counts the same no matter what is attached. It is the voltage and pulse height that controls the number of pulses being counted. This is unique for each probe attached to it.

So the meter is just counting pulses and displaying that count. The calibration you require is to adjust the voltage, pulse height for a particular probe to give you the calibration you desire. This must be done with a calibrated neutron source in your case so you are out of luck on that matter unless you can find a licensed source near you.

What most of us have done is what I mentioned in my first post. If your 2200 says 1273 volts and it works then that is a good place to be sure your meter is set to and putting out. Next is to put a gamma source (a small radioactive rock or similar) near the tube which does not have to be in the moderator. Make a note of the position of your threshold screw in case you want to restore it back. Start to take the threshold down until the meter spikes with counts with the gamma present. The meter should nearly go silent with the gamma source removed. Raise the threshold until the gamma counts JUST STOP when the source is near. At this point, the neutrons only will be counted and not the gammas. This should be the sweet spot for for proper neutron detection and should fit your calibration provided by Ludlum.

From what I see this is a Jun 2020 calibration on the Model 15, the neutron detector and the GM detector. (some body had the very big bucks!!!) Do not touch any thing!!!! You will only need to set your voltage and voltage alone!!!! Set it to that noted on the cal sheet for the probe used.

I assumed this set of three items were purchased new!!! Meaning all the probes with this instrument. If that is the case, the model 15 is good to go with each probe as long as the high voltages are set to the cal sheet voltage for each probe.

All the cal sheets with serial numbers indicate this model 15 serial number was indeed cal'd with these two probes in Late June. In theory you should just need to adjust the voltage only for the specific probe you have. (unless you have already twiddled with the pots) If this is the case, you will have to follow Frank's advice. If they cal'd the GM probe last you could tell by reading the voltage setting the moment you received it. If 900 volts, they did set the GM probe last. In this case, you need to readjust the pulse height for the neutron detector from its spec sheet. If you received it with the voltage set for the higher voltage of the neutron detector it is a simple plug and play scenario. No adjustments needed whatsoever

With the probe cal sheets alone, you should be able to use them on most any counter that allows you to set the HV and set the pulse heights to the spec sheet's tested value.

Richard Hull

Thanks Richard
The information was clear, i bought it for the neutron probe , i contacted too many russian companies and western companies the neutron detector only cost between 3 to 4 thousand $ , so i decide to go for used but really clean one .
The probe works fine with 2200. I will try to conect the other probes cnm-14 ,cnm-11 to ludlum 15.
In the worst scenario i can send it back to ludlum for calibration.
By the way I'm a poor dentist

Good man, the probe should work out great for you. The dentists in this country aren't exactly poor. I went for my check up two weeks ago and got a cleaning, and one composite filling for $380!

Richard Hull

Richard
Im not poor $
come, i will fix your all your teeth , in a week or two, and you adjust my devices.

LOL! THis thread has become too funny; certainly I needed that today - thanks!